A railroad frog is a device which is inserted at the intersection of a mainline rail and a turnout line rail to permit the flanges of wheels moving along one of the rails to pass across the other. The frog supports the wheels over the missing tread surface between the frog throat and the frog point and provides flangeways for aligning the wheels when passing over the point so that they will be afforded the maximum bearing area. Generally, standard turnout frogs may be classified as rigid frogs which have no movable parts or movable wing frogs in which one or both of the wings move outward to provide flangeways for railroad car wheels. The rigid frogs include manganese railbound frogs, solid manganese frogs and self guarded frogs. Movable frogs include railbound manganese spring frogs.
Rigid railbound manganese frogs are constructed by combining carbon steel rails with manganese steel castings. Railbound manganese spring frogs have a rigid, carbon steel, wing rail which encompasses a wing which is formed on a manganese steel cast insert and which is aligned substantially with a long point or heel rail connected to a turnout traffic rail and a flexible spring wing rail which is aligned substantially with a short point or heel rail which is connected to a mainline traffic rail.
Railbound manganese frogs are preferred over frogs which do not encompass manganese castings inasmuch as manganese steel has a resistance to abrasion and impact which exceeds that of carbon steel by as much as ten times.
In recent years, the frequency, the weight and the speed of rail traffic have increased. Consequently, the wear surfaces of manganese insert castings in railbound manganese frogs have been found to fail and become unacceptable for use within relatively short periods of time in certain zones. This increased wear and failure of the manganese insert casting has been found to occur primarily at three wheel transfer zones within the frog. The wear and failure occurs in these zones primarily because of wheel transfer impacts. Wheel transfer impacts normally occur as a result of an abrupt change in the path of a wheel and because of changes which occur in the wheel's profile as the wheel wears.
Railroad car wheels are made of either wrought steel or cast steel and have a carbon content of between 0.65% and 0.77% which approximately equals the carbon content of rail steel. Making the composition of railroad car wheels substantially the same as rails extends the wear life of both elements. However, when in use over a period of time the shape of a railroad car wheel changes substantially. This change in shape contributes greatly to failure of manganese insert castings caused by wheel transfer impacts as will be explained hereinbelow. The change in shape of a railroad car wheel with wear may be seen by referring to FIG. 3 of the drawings. This figure represents a part sectional view of the tread of a railroad car wheel. The dotted lines represent a new railroad car wheel whereas the solid lines depict a car wheel which has reached the condemning limits of wear and must be removed from service. When a wheel is new, the tread tapers inwardly from the inside of the flange to the outside edge of the wheel. This taper amounts to approximately one inch in twenty inches. In service, the inner vertical edge of the wheel flange bears against the gage side of a rail head, this being the side of the rail that faces the rail on the opposite side of the tie and the wheel tread bears against the top surface of a rail head. Consequently, the gage side of a wheel flange wears as does the tread of the wheel adjacent the flange. This wear may be seen by referring to FIG. 3 which illustrates the erosion of the gage side of the wheel flange and the loss of metal on the wheel tread adjacent the flange. The flange of a new wheel has a thickness of 1.375 inches and a depth of one inch. The wheel must be removed from service when the flange thickness decreases to 0.9375 inches or the flange depth increases to 1.50 inches. As a wheel wears, a false flange develops on the wheel opposite the flange which bears against the gage line of the rail. The false flange impacts the components of a manganese frog in the wheel transfer zones and contributes to or results in surface failure of the manganese insert castings.
As mentioned above, there are three primary transfer zones where the false flange formed on a worn railroad car wheel may cause damage to the manganese insert of a frog through impact. The first zone occurs at the toe end of the frog adjacent the throat of the insert. In this area the flange of a railroad car wheel transfers from a wing rail to a wing formed on the manganese insert as the wheel approaches the tip of the insert point moving in a facing direction. Movement in a facing direction for a railroad car wheel occurs as the wheel moves from the toe end of the frog to the heel end of a frog whereas a wheel undergoes a trailing direction movement when it passes from the heel end of a frog to the toe end of a frog. A second transfer zone where the false flange of a wheel may damage a surface of a manganese insert occurs as a wheel passes from a manganese wing to a running surface on the point of the insert. The third zone where the false flange on a railroad car wheel may impact a surface on the frog occurs at the heel end of the frog where a heel rail attaches to a heel extension formed at one end of the manganese insert point in alignment with the running surfaces of the point. In part, the impact is created by the physical discontinuity or gap which occurs at the interface of the manganese heel extension and the high carbon heel rail. In this location the traditional manganese casting has the smallest cross sectional area which gives rise to the greatest amount of wear.
Thus, it becomes desirable to provide manganese railroad frogs which accommodates worn railroad car wheels having false flanges in such a manner that the false flanges are prevented from impacting surfaces on the manganese casting to prevent unnecessary wear.